The present invention relates to data communications equipment and, more particularly, to the use of a side-channel in a simultaneous voice and data communications system.
The co-pending, commonly assigned, U.S. Patent application of Gordon Bremer and Kenneth D. Ko entitled "Simultaneous Analog and Digital Communication," Ser. No. 08/076505, now U.S. Pat. No. 5,448,555, issued Sep. 5, 1995, filed on Jun. 14, 1993, describes a simultaneous voice and data communications system in which a voice signal is added to a data signal for transmission over a communications channel to a receiving modem.
In this simultaneous analog and digital communication system, the data signal to be transmitted is represented by a sequence of data symbols, where each data symbol is associated with a particular N-dimensional signal point value taken from a signal space. Similarly, the analog signal, which is represented by a voice signal, is processed so that it is mapped into the N-dimensional signal space to provide a voice signal point. This voice signal point defines the magnitude and angle of a voice signal vector about the origin of the signal space. The data symbol and the voice signal vector are then added together to select a resultant N-dimensional signal point, which is then transmitted to a far-end modem.
Upon reception of the transmitted N-dimensional signal point, the receiver of the far-end modem detects the embedded data symbol and subtracts the data symbol from the received N-dimensional signal point to yield the voice signal vector. This voice signal vector is then used to recreate the voice signal.
Using this above-mentioned technique to simultaneously transmit voice and data, there is sometimes a need to transmit additional information separate and apart from the voice and data information. For example, the co-pending, commonly assigned, U.S. patent application of Gordon Bremer, Kenneth D. Ko, Luke J. Smithwick, and Edward S. Zuranski, entitled "Autorate Method for Simultaneous Transmission of Voice and Data," Ser. No. 08/076,525, filed on Jun. 21, 1993, now abandoned, describes that a "silence indicator" message can be additionally transmitted on a secondary, or side-channel, as is known in the art, where this side-channel is separate and apart from the simultaneous voice and data transmission.